Gloss measurement apparatus and gloss measurement method

Abstract

A gloss measurement apparatus which emits light from a light source and finds an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured. The gloss measurement apparatus is provided with an acquisition component, a pixel gloss value calculation component and an evaluation value calculation component. The acquisition component acquires image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured. The pixel gloss value calculation component calculates gloss values of the respective pixels on the basis of the received light amounts at the respective pixels of the image information acquired by the acquisition component. The evaluation value calculation component calculates the evaluation value representing the glossiness of the object to be measured on the basis of the gloss values calculated by the pixel gloss value calculation component.

1. A gloss measurement apparatus that emits light from a light source and finds an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured, the gloss measurement apparatus comprising:
 an acquisition component, which acquires image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured; 
 a pixel gloss value calculation component, which calculates gloss values of the respective pixels on the basis of the received light amounts of the respective pixels of the image information acquired by the acquisition component; and 
 an evaluation value calculation component, which calculates the evaluation value representing glossiness of the object to be measured on the basis of the gloss values calculated by the pixel gloss value calculation component, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     2. The gloss measurement apparatus of  claim 1 , wherein the evaluation value calculation component comprises a distribution calculation component, which calculates a distribution of pixel counts for respective gloss values from the gloss values of the respective pixels,
 and the evaluation value calculation component identifies a gloss value at which a number of pixels, which is summed from a side of high gloss value in the distribution calculated by the distribution calculation component, reaches a predetermined number, and calculates the evaluation value representing glossiness of the object to be measured on the basis of a total gloss value, the total gloss value being a sum of gloss values of the respective pixels at and above the identified gloss value. 
 
   
   
     3. The gloss measurement apparatus of  claim 1 ,wherein the evaluation value calculation component comprises an index value calculation component which, on the basis of the gloss values of the respective pixels, calculates an average gloss index value representing an average value of gloss values of all the pixels and a gloss nonuniformity index value representing a degree of occurrence of gloss nonuniformities,
 and the evaluation value calculation component calculates the evaluation value representing glossiness of the object to be measured by multiplying the average gloss index value and the gloss nonuniformity index value with respective predetermined weighting coefficients, and 
 finding a linear sum of values obtained by the multiplication, 
 such that the evaluation value representing glossiness of the object to be measured increases when the average gloss index value increases and the evaluation value representing glossiness of the object to be measured increases when the gloss nonuniformity index value increases. 
 
   
   
     4. The gloss measurement apparatus of  claim 3 , wherein the gloss nonuniformity index value is a value found by dividing a standard deviation value of the gloss values of the respective pixels by the average gloss index value. 
   
   
     5. The gloss measurement apparatus of  claim 1 , further comprising a correction component, which performs a correction to cause a spatial frequency characteristic of the gloss values of respective pixels which have been calculated by the pixel gloss value calculation component to correspond with a spatial frequency characteristic of human vision,
 wherein the evaluation value calculation component calculates the evaluation value representing glossiness of the object to be measured on the basis of the gloss values of respective pixels which have been corrected by the correction component. 
 
   
   
     6. The gloss measurement apparatus of  claim 5 , wherein the correction component comprises:
 a two-dimensional Fourier transform component, which applies a two-dimensional Fourier transformation to the gloss values of the respective pixels which have been calculated by the pixel gloss calculation component, for converting the gloss values to gloss values in a spatial frequency domain; 
 a multiplication component, which multiplies a predetermined visual transfer function, which corresponds to the spatial frequency characteristic of human vision, with frequency information representing the gloss values of the respective pixels which have been converted to spatial frequency domain gloss values by the two-dimensional Fourier transform component; and 
 a two-dimensional inverse Fourier transform component, which applies a two-dimensional inverse Fourier transformation to results of the multiplication by the multiplication component, for converting the multiplication results to gloss values of respective pixels which are pixels in an image space domain. 
 
   
   
     7. A gloss measurement method that emits light from a light source and finds an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured, the method comprising:
 acquiring image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured; 
 calculating gloss values of the respective pixels on the basis of the received light amounts of the respective pixels of the acquired image information; and 
 calculating the evaluation value representing glossiness of the object to be measured on the basis of the calculated gloss values, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     8. A storage medium readable by a computer, the storage medium storing a gloss measurement program including instructions which are executable by the computer to perform a function for:
 emitting light from a light source; acquiring image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light which is reflected by an object to be measured; and finding an evaluation value, which represents a glossiness of the object to be measured, on the basis of the acquired image information, the function comprising: 
 a pixel gloss value calculation step that calculates gloss values of the respective pixels on the basis of the received light amounts of the respective pixels of the acquired image information; and 
 an evaluation value calculation step that calculates the evaluation value representing glossiness of the object to be measured on the basis of the gloss values calculated by the pixel gloss value calculation step, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     9. A gloss measurement apparatus that emits light from a light source and finds an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured, the gloss measurement apparatus comprising:
 a specular reflection image information acquisition component, which acquires specular reflected light image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured; and 
 a calculation component, which calculates the evaluation value representing glossiness of the object to be measured on the basis of the specular reflected light image information acquired by the specular reflection image information acquisition component, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     10. The gloss measurement apparatus of  claim 9 , further comprising a diffuse reflection image information acquisition component, which acquires diffuse reflected light image information in accordance with received light amounts, at predetermined respective pixels, of diffuse reflected light which, of the light emitted from the light source, has been diffusely reflected by the surface of the object to be measured,
 wherein the calculation component calculates the evaluation value representing glossiness of the object to be measured on the basis of the specular reflected light image information acquired by the specular reflection image information acquisition component and the diffuse reflected light image information acquired by the diffuse reflection image information acquisition component. 
 
   
   
     11. The gloss measurement apparatus of  claim 10 , wherein the light source emits light including a predetermined incidence angle deviation about an optical axis of the light that is incident at the surface of the object to be measured. 
   
   
     12. The gloss measurement apparatus of  claim 10 , wherein the calculation component comprises:
 a luminance calculation component, which calculates luminances of specular reflected light at respective pixels on the basis of the received light amounts of the respective pixels represented by the specular reflected light image information, and calculates luminances of diffuse reflected light at respective pixels on the basis of the received light amounts of the respective pixels represented by the diffuse reflected light image information; 
 a first physical quantity calculation component, which calculates a first physical quantity, which corresponds to a luminance difference between specular reflected light and diffuse reflected light, on the basis of the specular reflected light and diffuse reflected light luminances calculated by the luminance calculation component; 
 a second physical quantity calculation component, which calculates a second physical quantity, which corresponds to nonuniformities in luminance of the specular reflected light, on the basis of the specular reflected light luminances calculated by the luminance calculation component; and 
 an evaluation value calculation component, which calculates the evaluation value representing glossiness of the object to be measured, by 
 multiplying the first physical quantity and the second physical quantity with respective predetermined weighting coefficients and 
 finding a linear sum of values obtained by the multiplication. 
 
   
   
     13. The gloss measurement apparatus of  claim 12 , wherein the luminance calculation component
 divides the received light amounts of the respective pixels represented by the specular reflected light image information by a light-receiving time of the specular received light, and calculates the specular reflected light luminances on the basis of received light amounts per unit time that are obtained by this division, and 
 divides the received light amounts of the respective pixels represented by the diffuse reflected light image information by a light-receiving time of the diffuse received light, and calculates the diffuse reflected light luminances on the basis of received light amounts per unit time that are obtained by this division. 
 
   
   
     14. The gloss measurement apparatus of  claim 13 , further comprising a standard surface luminance storage component, which stores a luminance of specular reflected light at a standard surface which is used in measurement of specular gloss,
 wherein the luminance calculation component calculates the specular reflected light luminances of respective pixels and the diffuse reflected light luminances of respective pixels as values which are normalized in accordance with the luminance of specular reflected light at the standard surface. 
 
   
   
     15. The gloss measurement apparatus of  claim 12 , wherein the first physical quantity calculation component calculates an average value of luminances of respective pixels that are at and above a middle value between a maximum luminance and a minimum luminance, of the specular reflected light luminances of respective pixels, and calculates the first physical quantity on the basis of this average value and an average value of the diffuse reflected light luminances of the respective pixels. 
   
   
     16. The gloss measurement apparatus of  claim 12 , wherein the second physical quantity calculation component applies a two-dimensional Fourier transformation to the specular reflected light luminances at the respective pixels for converting the luminances to luminances in a spatial frequency domain, and divides an integrated value, into which the thus obtained specular reflected light luminances at respective pixels in the spatial frequency domain are integrated over all frequencies, by an average value of the specular reflected light luminances at the respective pixels, for calculating the second physical quantity. 
   
   
     17. The gloss measurement apparatus of  claim 10 , further comprising:
 a stage, which includes a stage surface which retains the object to be measured; 
 a first translation component, which translates the light source, the specular reflection image information acquisition component and the diffuse reflection image information acquisition component in a predetermined direction, which is parallel with the stage surface; and 
 a second translation component, which translates the stage in a direction intersecting the predetermined direction. 
 
   
   
     18. The gloss measurement apparatus of  claim 17 , further comprising an angle alteration component, which alters an angle that is formed between the light source and the specular reflection image information acquisition component about a normal line from an incidence position on the stage surface of the light emitted from the light source. 
   
   
     19. The gloss measurement apparatus of  claim 17 , further comprising a normal direction movement component, which relatively moves the light source, the specular reflection image information acquisition component and the diffuse reflection image information acquisition component in a normal direction of the stage surface with respect to the stage. 
   
   
     20. The gloss measurement apparatus of  claim 17 , wherein the stage comprises an electrostatic adherence plate which adheres and retains the object to be measured by electrostatic force. 
   
   
     21. The gloss measurement apparatus of  claim 17 , further comprising a laser output component, which outputs laser light to an incidence position on the stage surface of the light emitted from the light source. 
   
   
     22. The gloss measurement apparatus of  claim 10 , further comprising:
 a stage, which includes a stage surface which retains the object to be measured; 
 an r-direction movement component, which moves the light source, the specular reflection image information acquisition component and the diffuse reflection image information acquisition component in a radial r-direction of polar-co-ordinates, an origin point of which is an incidence position on the stage surface of the light emitted from the light source; and 
 a θ-direction rotation component, which rotates the light source, the specular reflection image information acquisition component and the diffuse reflection image information acquisition component in a rotation angle θ direction. 
 
   
   
     23. The gloss measurement apparatus of  claim 10 , wherein the light source comprises:
 a halogen fiber light source, which emits light; 
 a condensing lens, which condenses the light emitted from the halogen fiber light source; and 
 a diffuser, which diffuses the light that has been condensed by the condensing lens. 
 
   
   
     24. A gloss measurement method that emits light from a light source and finds an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured, the method comprising:
 acquiring specular reflected light image information in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured; and 
 calculating the evaluation value representing glossiness of the object to be measured on the basis of the acquired specular reflected light image information, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     25. The gloss measurement method of  claim 24 , further comprising acquiring, in addition to the specular reflected light image information, diffuse reflected light image information in accordance with received light amounts, at predetermined respective pixels, of diffuse reflected light which, of the light emitted from the light source, has been diffusely reflected by the surface of the object to be measured, and
 calculating the evaluation value representing glossiness of the object to be measured on the basis of the acquired specular reflected light image information and the acquired diffuse reflected light image information. 
 
   
   
     26. A storage medium readable by a computer, the storage medium storing a gloss measurement program including instructions which are executable by the computer to perform a function for
 emitting light from a light source and finding an evaluation value, which represents a glossiness of an object to be measured, on the basis of specular reflected light which is reflected by the object to be measured, the function comprising: 
 a storage step, for storing specular reflected light image information at an image information storage component, the specular reflected light image information being acquired in accordance with received light amounts, at predetermined respective pixels, of specular reflected light from a surface of the object to be measured; and 
 an evaluation value calculation step, for calculating the evaluation value representing glossiness of the object to be measured on the basis of the specular reflected light image information which has been stored at the image information storage component, 
 wherein the gloss value for each of the pixels is calculated by summing values obtained by multiplying respectively different coefficients with each of light amounts of R, G, B for each of the pixels, and the different coefficients are determined by imaging a sample of which the specular gloss value is already known, finding average values of the light amounts of R, G, B of the pixels from the sample, and performing regression analysis using the average values and the known specular gloss value. 
 
   
   
     27. The storage medium of  claim 26 , wherein the storage step further includes storing diffuse reflected light image information at the image information storage component, the diffuse reflected light image information being acquired in accordance with received light amounts, at predetermined respective pixels, of diffuse reflected light which, of the light emitted from the light source, has been diffusely reflected by the surface of the object to be measured, and
 the evaluation value calculation step includes calculating the evaluation value representing glossiness of the object to be measured on the basis of the specular reflected light image information and the diffuse reflected light image information which have been stored at the image information storage component.